Abstract
Pseudogley soils are the most typical types of the heavy clayey soils distributed over the coastal terraces in northern Hokkaido. Its moisture regimes and some problems on drainage and soil improvements have been discussed based on field experiments on Komukai pseudogley soil. The conclusions are as follows : The physical properties that is closely related to drainage of pseudogley soils are an existence of the impermeable layers in shallower horizon, small capacity of water storage, and low unsaturated hydraulic conductivity in subsoils. Further characteristic properties of pseudogley soils are lateral flow of excessive gravitational water above the impermeable layers through the cracks of Bg horizons into lower parts of slopes or slightly depressed grounds causing a swampy area and difficulty in drainage. For the purpose of drawdown of the stagnant water table (perched water table), the tile drainage and open ditch drainage are fundamental and essential. Subsoiling with panbreaker is highly effective for the improvent of uneven drainage caused by slight change in relief and a variation of distance from drain tubes. Drainage in unsaturated layers is importanant for trafficability and tillage operations. Drawdown of the perched water table, deep plowing and sand dressing have some effects for its improvement. Drainage of pseudogley soils is ineviteble for land use, but in dry seasons it often promotes drought injury. Deep plowing and subsoil plowing increase the water storage and availability of moisture for plants to some extent.
